German police said on Sunday they had ended a major operation launched after they received information about a possible threat of an attack in the south-western town of Offenburg on Saturday night.

Armed police patrol at the Christmas market outside the Centro, one of Germany's largest shopping and leisure centers, in Oberhausen, western Germany in this representative file photo from December 23, 2016. (AFP Photo)

German police said on Sunday they had ended a major operation launched after they received information about a possible threat of an attack in the south-western town of Offenburg on Saturday night.

Officers stepped up security in the town centre and on public transport and police said one possible target was a night club which was not named. Investigations were continuing but no further details on the nature of the threat were available.

A spokesman in Offenburg, in the state of Baden-Wuerttemberg and close to the French border, did not give any further details.

Germany is on high alert following deadly militant Islamist attacks in France and Belgium and after a failed asylum seeker from Tunisia drove a truck into a Berlin Christmas market in December, killing 12 people.

On Saturday, police in the city of Essen closed a shopping mall after security services warned of a possible attack.